Polarizing plate

ABSTRACT

A polarizing plate with which, not only suppression in a drop in polarization efficiency, but also with which hue shift and light leakage do not substantially occur, under a high humidity/high temperature environment is provided. The polarizing plate of the present invention includes a polyvinyl-alcohol-based polarizing film, a protective film mainly composed of a cyclic-olefin-based resin and laminated on at least one side of the polarizing film, and an anchor coat agent film and an adhesive layer interposed between the polarizing film and the protective film. The amount of change in optical in-plane retardation of the protective film is 5 nm or less, after 24 hours in an atmosphere of 80° C., and the wetting tension of the laminated surface is 500 μN/cm (23° C.) or more. The anchor coat agent is made of polyester polyol and polyisocyanate, and the adhesive layer is made of polyvinyl-alcohol-based adhesive.

TECHNICAL FIELD

The present invention relates to a polarizing plate, particularly to apolarizing plate having high durability and high polarization efficiencythat is useful for liquid crystal displays (LCDs) and more specifically,to an improvement in a polarizing plate for preventing drop inpolarization efficiency, hue shift, and light leakage under a highhumidity/high temperature environment.

BACKGROUND ART

A conventional polarizing plate with high polarization efficiency isgenerally such that a cellulose-triacetate-based (hereinafter, referredto as is TAC) film, which serves as a protective film, is laminated on apolarizing film in which iodine or a dichroic dye is adsorbed andoriented in a polyvinyl-alcohol-based (hereinafter, referred to as PVA)film, with an aqueous solution of PVA resin, which serves as anadhesive, in a state of wet or semidry flowability.

However, since the water absorption and water vapor permeability of TACis high, in a polarizing plate using TAC for the protective film,deterioration in polarization performance under a high humidity/hightemperature environment, specifically, drop in polarization efficiency,hue shift, and light leakage under crossed nicols, has been significant.

In order to overcome these problems, polarizing plates that use a filmmade of a resin with low water absorption and low water vaporpermeability for the protective film have been proposed.

For example, Japanese Unexamined Patent Publication No. 7-77608discloses a polarizing plate such that a film serving as a protectivefilm and made of a thermoplastic saturated norbornene-based resin isadhered to a PVA-based polarizing film using an acrylic-based adhesiveor a polyester-isocyanate-based adhesive. After such a polarizing plateis subjected to an environment of 80° C. and 90% RH for 500 hours, thepolarization efficiency is 95% or higher and the single transmissivity38% or higher.

In addition, Japanese Unexamined Patent Publication 7-294732 discloses apolarizing plate such that a film having a photoelastic coefficient of25.0×10⁻¹³ cm²/dyne or less, for example, a film made of an amorphouspolyolefin such as Zeonex, or polymethyl methacrylate serves as asupport for a polarizing element film, and the support is adhered to thepolarizing element film using an acrylic-based adhesive. After such apolarizing plate is subjected to an environment of 60° C. and 90% RH for100 hours, the pyschometric lightness is small.

However, although these polarizing plates are able to suppress a drop inpolarization efficiency under a wet heat environment, it cannot be saidthat suppression of hue shift and light leakage is sufficientlyrealized.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a polarizing platewith which, not only suppression of a drop in polarization efficiency isachieved, but also with which hue shift and light leakage do notsubstantially arise, under a high temperature/high humidity environment.

A polarizing plate of the present invention comprises apolyvinyl-alcohol-based polarizing film, a protective film mainlycomposed of a cyclic-olefin-based resin and laminated on at least oneside of the polarizing film, an anchor coat agent layer, and an adhesivelayer, the anchor coat agent layer and the adhesive layer interposedbetween the polarizing film and the protective film, wherein the amountof change in optical in-plane retardation of the protective film is 5 nmor less after 24 hours in an atmosphere of 80° C., and the wettingtension of the laminated surface of the protective film is 500 μN/cm(23° C.) or more, the anchor coat agent is made of polyester polyol andpolyisocyanate, and the adhesive layer is made ofpolyvinyl-alcohol-based substances.

The polarizing film utilized in the present invention is produced byuniaxially stretching and orienting a film made of PVA or a derivativethereof, and subsequently, adsorbing iodine, carrying out a boric acidsolution treatment, and drying the film while under tension. Such a filmalso may be produced by immersing a film made of PVA or a derivativethereof in an aqueous solution of iodine such that the iodine isadsorbed, and subsequently, uniaxially stretching and orienting the filmin a boric acid solution and drying the film while under tension.Polarizing films that utilize dichroic dyes, such as those that areazo-based, anthraquinone-based, and tetrazine-based, instead of iodineare fabricated in the same manner as well.

The polarization efficiency of a polarizing film obtained in such amanner is preferably, 95.0% or higher, more preferably, 99.0% or higher,and ever more preferably, 99.7% or higher.

Hue shift as referred to in the present invention denotes a phenomenonsuch that when a single polarizing plate or crossed nicols is placed ina dry heat atmosphere or a wet heat atmosphere, hue shift occurs withthe single polarizing plate or the crossed nicols.

When a liquid crystal display employing polarizing plates with which hueshift arises is used for a long period, the hue of the display changesand contrast deteriorates, becoming one cause of deterioration in theperformance of the liquid crystal display.

Light leakage as referred to in the present invention denotes aphenomenon such that in-plane luminance changes when two polarizingplates arranged to have a crossed nicols relation are placed in a wetheat environment.

When a liquid crystal display that employs polarizing plates thatgenerate light leakage is used for a long period, light leaks at theedges of the display when black is displayed, and thereby displaycontrast deteriorates, becoming one cause of deterioration in theperformance of a liquid crystal display.

Having fully considered how to provide a polarizing plate with which,not only suppression of a drop in polarization efficiency is achieved,but also with which hue shift and light leakage do not substantiallyarise, under a high temperature/high humidity environment, the presentinventors came to the following conclusion, by which the presentinvention was achieved.

First, suppression of a drop in polarization efficiency under a hightemperature/high humidity environment can be achieved by using a filmwith low water absorption and low water vapor permeability for theprotective film of a polarizing plate. Suppression of hue shift under ahigh temperature/high humidity environment can be realized bysufficiently adhering a polarizing film and a protective film and bysuppressing reversion in the alignment of the polarizing film.Suppression of light leakage under a high temperature/high humidityenvironment can be realized by using a film having a small amount ofchange in optical in-plane retardation for the protective film of apolarizing plate.

The present inventors then fully considered how to substantiate theseinferences.

For the present invention, a film mainly composed of cyclic-olefin-basedresin was employed for the protective film of the polarizing plate,because such a film has low water absorption and low water vaporpermeability, and various physical properties required of a protectivefilm for a polarizing plate, such as light transmissivity. (In addition,because cyclic-olefin-based resin has a small photoelastic coefficient,it was conjectured to be useful in preventing light leakage.)

In the present invention, cyclic-olefin-based resin is used as a generalterm, specific examples (a) to (d) being shown below.

(a) polymers that are ring-opening (co-)polymers of cyclic olefin withhydrogen added as needed

(b) (co-)polymers with cyclic olefin attached

(c) random copolymers of cyclic olefin and an α-olefin such as ethyleneor propylene

(d) graft modified substances that result when the above (a) to (c) aremodified with unsaturated carboxylic acid or derivatives thereof

The cyclic olefin is not particularly limited, examples includingnorbornene, tetracyclododecene, and derivatives thereof (for example,substances containing a carboxyl group or an ester group).

Known additives such as ultraviolet absorbers, organic or inorganicantiblocking agents, slip additives, antistatic agents, and stabilizersmay be added appropriately to the cyclic-olefin-based resin.

The method of forming a protective film from cyclic-olefin-based resinis not particularly limited, it being possible to employ methods such assolution casting, extrusion, and calendering.

Examples for a solvent used in solution casting include alicyclichydrocarbons such as cyclohexane and cyclohexene and derivativesthereof, as well as aromatic hydrocarbons such as toluene, xylene, andethyl benzene and derivatives thereof.

The thickness of the protective film is commonly 5–150 μm, preferably10–100 μm, and more preferably 30–70 μm. When thickness is too thin, afilm tends to be difficult to handle and when thickness is too thick,the amount of change in optical in-plane retardation tends to be large.

In order to determine the relationship between hue shift and theadhesive strength of a protective film/polarizing film under a hightemperature/high humidity environment, tests were carried out usingvarious adhesives with varying adhesive strength, and as was initiallypredicted, it was determined that there is a correlation between hueshift and the adhesive strength of a protective film/polarizing film.However, there was no adhesive with which hue shift substantially didnot occur. In consideration of this, the present inventors consideredvarious ways of increasing the adhesive strength and suppressing hueshift to the greatest possible degree and eventually, discovered twoways of overcoming the problems of adhesive strength and hue shift.

Specifically, first the wetting tension of the surface of the protectivefilm to be laminated with the polarizing film is made to be 500 μN/cm(23° C.) or higher and preferably 550 μN/cm (23° C.) or higher. In orderto achieve this value, it is not necessary to employ a particulartechnique, it being possible to use a technique known in the art.Examples for a surface treatment include a corona discharge treatment,an ultraviolet irradiation treatment, and a chemical treatment. Thecorona discharge treatment or ultraviolet irradiation treatment may becarried out in air or in an atmosphere of nitrogen or a rare gas.

When the wetting tension is less than 500 μN/cm (23° C.), sufficientadhesive strength cannot be obtained.

Secondly, an anchor coat agent made of polyester polyol andpolyisocyanate is coated on the protective film surface and dried, andsubsequently, an adhesive solution of polyvinyl-alcohol-based substancesis adhered to the polarizing film in a wet or semidry state.

The coating and drying of the anchor coat agent may be carried outdirectly before the adhering with the protective film and the polarizingfilm an adhesive solution, or the film may be wound temporarily aftercoating the protective film surface with the anchor coat agent anddrying, and the adhering of the protective film and polarizing film withan adhesive solution carried out at a later time.

The polyester polyol of the anchor coat agent has ester bonds in itsmolecules and two or more hydroxyl groups in each molecule, and thepolyisocyanate of the anchor coat agent has two or more isocyanategroups in each molecule. The skelton structure of the polyisocyanate maybe an aromatic ring or another structure, a long chain alkylene groupbeing more preferable from the perspective of adhesive strength. This isthought to be because long-chain alkylene has a degree of flexibilityand thus good adhesion with the protective film surface is expected. Itis preferable that the anchor coat agent be in the form of an emulsionor solution.

The mixing ratio of polyester polyol and polyisocyanate is preferably,20:1–1:20 and more preferably, 5:1–1:5, in consideration of theequivalence weight ratio of the hydroxyl groups and the isocyanategroups.

It is preferable that the amount of anchor coat agent be such that athickness after drying of 0.001–5 μm results and more preferable that athickness of 0.01–2 μm results. When too little anchor coat agent isused, adhesive strength often cannot be realized to the degree desired,and when too much is used, coating nonuniformities easily arise, whichis often undesirable in terms of hue shift and light leakage.

Note that it cannot be said that substances that react withpolyisocyanate other than polyester polyol mentioned above, for example,acrylic-based substances, sufficiently demonstrate advantageous effectsin terms of suppressing hue shift.

The polyvinyl-alcohol-based substances of the adhesive are mainlycomposed of a resin that is obtained by carrying out a saponificationtreatment on vinyl acetate resin. It is preferable that the degree ofpolymerization be 1000–3000 and that the degree of saponification be 94%or higher and more preferable that the degree of polymerization be1500–3000 and the degree of saponification be 98% or higher. Othermonomers such as monomers copolymerized appropriately with a smallamount of acrylic acid, crutonic acid, itaconic acid, and the like ormonomers modified by alkyl groups, epoxy groups, or the like may beused.

It is preferable that the amount of adhesive solution be such that athickness after drying of 0.01–10 μm results, more preferable that athickness after drying of 0.02–5 μm results, and even more preferablethat a thickness after drying of 0.05–3 μm results. When too littleadhesive is used, adhesive strength often cannot be realized to thedegree desired, and when too much is used, coating nonuniformitieseasily arise, which is often undesirable in terms of hue shift and lightleakage.

A substance that induces reactive curing with polyvinyl alcohol, such aspolyisocyanate, boric acid, alkylene diamine, and epoxy resin, may beadded. Advantageous effects are obtained particularly withpolyisocyanate.

In order to determine the relationship between light leakage and theamount of change in optical in-plane retardation under a hightemperature/high humidity environment, protective films having varyingamounts of change in optical in-plane retardation, thicknesses of 50 μm,and mainly composed of various cyclic-olefin-based resins, were formed,and polarizing plates were fabricated using these protective films.Investigation into the amount of light leakage using a method describedlater revealed that there is a correlation between light leakage and theamount of change in optical in-plane retardation, as was initiallypredicted, and it was discovered that light leakage substantially doesnot occur when the amount of change in optical in-plane retardation is 5nm or less.

In the tests, substances described previously were used for thelaminated surface of the protective film, the anchor coat agent, and theadhesive.

The amount of change in optical in-plane retardation was obtained asfollows. As shown in FIG. 2( a), a protective film 3 was cut to a sizelength×width=100 mm×100 mm, and this film was attached to a glasssubstrate 1 with a binder 2 made of acrylester-based base resin and anisocyanate-based curing agent. The optical in-plane retardation wasmeasured in each of nine sections divided as shown in FIG. 2( b), andthe average value R₀ was obtained. After then subjecting this to an 80°C. atmosphere for 24 hours, the optical in-plane retardation wasmeasured in the same nine sections, and the average value R wasobtained. The difference between R and R₀ (R−R₀) was taken to be theamount of change in optical in-plane retardation.

For the most part, the amount of change in optical in-plane retardationis dependent on distortion of molecular chains in the protective filmand on residual shrinkage percentage.

When production of a protective film is realized by solution casting,distortions in the molecular chains arise in the drying step. Inaddition, residual shrinkage percentage is affected by the orientationof the cyclic-olefin-based resin when the solution is stretched on ametal drum or an endless belt, by the orientation of cyclic-olefin-basedresin caused by pulling tension in the drying step, and by the residualsolvent.

When the production of a protective film is realized by extrusion,distortions in the molecular chains arise during cooling and hardeningwith a chill roll after extrusion from an extruder. In addition,residual shrinkage percentage is affected by the draw during extrusionfrom the extruder and by the orientation of the cyclic-olefin-basedresin caused by pulling tension from the point of cooling and hardeningto the point of winding.

In order to make the amount of change in optical in-plane retardation ofthe protective film 5 nm or less, it is necessary to correct distortionsin molecular chains in the protective film by a suitable method and toreduce the residual shrinkage percentage.

For example, methods of correcting distortions of molecular chains andof reducing the residual shrinkage percentage include heating the filmunder a minus draw before winding the film and leaving the loosely woundfilm in a heat chamber. In the case of employing solution casting forproduction, leaving the film in a drying oven for a long period is onemethod of reducing the residual solvent, preferably until none remains.Adding preferably 0.1–20% by weight, more preferably 0.5–10% by weight,and even more preferably 0.5–5% by weight with respect to resin of aplasticizer such as dioctyl adipate, dioctyl phthalate, or isodecyladipate to the casting solution before hand is another method. Becausethe drying time required for practically eliminating the residualsolvent is reduced by ⅕– 1/20 when a plasticizer is added, such a methodis advantageous from the perspective of productivity and cost ofequipment. The advantageous effects of adding a plasticizer areconjectured to be as follows. That is, it is thought that becausecyclic-olefin-based resin molecules have a bulky skelton structure,solvent that enters into these gaps does not easily evaporate, but whena plasticizer is added, the plasticizer enters so as to discharge thesolvent from the gaps.

The residual shrinkage percentage necessary in order to make the amountof change in optical in-plane retardation of the protective film 5 nm orless is such that surface shrinkage percentage according to a measuringmethod described later is preferably 0.8% or less, more preferably 0.5%or less, and even more preferably, 0.3% or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is lateral view of the arrangement of a polarizing plate whenin-plane luminance of the polarizing plate is measured, and FIG. 1( b)is a plan view of the same.

FIG. 2( a) is a lateral view of the arrangement of a polarizing platewhen in-plane optical retardation is measured, and FIG. 2( b) is a planview of the same.

DESCRIPTION OF THE REFERENCE NUMERALS

1 glass substrate

2 binder

3 protective film

4 polarizing plate

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, typical examples of the present invention aredescribed along with comparative examples.

The method of measuring and method of evaluating physical propertiesemployed in the present invention are as follows.

Water absorption was measured at 23° C. for 24 hrs. using an ASTM D570.

Water vapor permeability was measured at 40° C. and 90% RH using theMocon test (Permatran-W600 water permeability measurement deviceavailable from Mocon, Inc.).

Wetting tension was measured in compliance with JIS-K6768.

The amount of change in optical in-plane retardation was measured usingthe following method. Specifically, as shown in FIG. 2( a), a protectivefilm 3 cut to a size length×width=100 mm×100 mm is adhered to a glasssubstrate 1 with a binder 2 made of acrylester-based base resin and anisocyanate-based curing agent interposed. Using a birefringence analyzer(Kobra automated birefringence analyzer available from Oji Keisoku,Inc.), optical in-plane retardation was then measured in each of ninesections, as shown in FIG. 2( b), and the average value R₀ was obtained.Note that the arrows in the figure indicate the longitudinal directionof the protective film 3. After then subjecting this to an 80° C.atmosphere for 24 hours, the optical in-plane retardation was measuredin the same nine sections, and the average value R was obtained. Thedifference between R and R₀ (R−R₀) was taken to be the amount of changein optical in-plane retardation.

The surface shrinkage percentage was measured using the followingmethod. Specifically, a single protective film was cut to a sizelength×width=100 mm×100 mm, and after subjecting the film to an 80° C.atmosphere for 100 hours, the surface shrinkage percentage wasdetermined from Equation (1) below, where M is the length (mm) and T isthe width (mm).

$\begin{matrix}{{\begin{matrix}\text{Surface~~Shrinkage} \\\text{Percentage}\end{matrix}(\%)} = {{\left\{ {\left( {100 \times 100} \right) - \left( {M \times T} \right)} \right\} \div \left( {100 \times 100} \right)} \times 100}} & (1)\end{matrix}$

The polarization efficiency of polarizing plates was determined usingthe following method. Specifically, two polarizing plates were arrangedon top of one another so that the polarization axes were oriented in thesame direction, and Ti₁ was taken to be the average value for lighttransmissivity measured continuously from a wavelength of 400 nm to a700 nm using a spectrophotometer. Two polarizing plates were thenarranged so that the polarization axes were perpendicular to oneanother, and T₂ was taken to be the average value for lighttransmissivity measured in the same manner. Polarization efficiency wasthus determined from Equation (2) below. A higher numerical valueindicates better polarization performance.

$\begin{matrix}{\text{polarization~~efficiency~~(\%)} = {\sqrt{\frac{T_{1} - T_{2}}{T_{1} + T_{2}}} \times 100}} & (2)\end{matrix}$

The single transmissivity of the polarizing plates is the average valuefor the light transmissivity of one polarizing plate measuredcontinuously from a wavelength of 400 nm to a 700 nm using aspectrophotometer. A higher numerical value indicates bettertransparency of the polarizing plates.

The humidity and heat resistance test of the polarization efficiency ofthe polarizing plates was carried out using the method below.Specifically, a polarizing plate was subjected to an atmosphere of 80°C. and 90% RH for 48 hours. The retention of the polarization efficiencyis a value obtained by dividing the polarization efficiency after thetest by the polarization efficiency before the test. A higher numericalvalue indicates better humidity and heat resistance.

Measurement and evaluation of hue shift were carried out using thefollowing method. Specifically, using SZ-Σ80II available from NipponElectric Industries Co., Ltd., a value “a” and a value “b” for a singlepolarizing plate were measured before and after subjecting thepolarizing plate to an atmosphere of 80° C. and 90% RH for 24 hoursaccording to the Hunter-Lab method. A greater amount of change in value“a” or a greater amount of change in value “b” indicates a greater hueshift.

Light leakage was evaluated using the in-plane luminance of a polarizingplate. Measurement and evaluation of the in-plane luminance ofapolarizing plate are carried out as follows. Specifically, as shown inFIG. 1( a), two polarizing plates 4 of dimensions 100 mm×100 mm cut froma long polarizing plate at an angle of 45° with respect to thepolarization axis were adhered to either side of a glass substrate 1with a binder 2 interposed so that the polarization axes wereperpendicular to one another, and this structure was subject to anatmosphere of 80° C. and 90% RH for 24 hours. Subsequently, thisstructure was arranged on a backlight (Fuji Color Light Box 5000available from Fuji Color Trading Co., Ltd.), the light source from thebacklight was set to 100% reference value, and luminance was measured ineach of nine sections divided as shown in FIG. 1( b), using a luminancemeter (LS-100 available from Minolta Co., Ltd.). Using the resultingvalues, the amount of light leakage as shown by Equation (3) below wasdetermined. In this case, a closer numerical value to 1 indicates lesslight leakage.

$\begin{matrix}{\begin{matrix}\text{Amount~~of} \\\text{Light~~Leakage}\end{matrix} = {\left( {\begin{matrix}\text{Average} \\\text{Luminance~~of}\end{matrix}\mspace{25mu} 2{◯4◯6◯8◯}} \right) \div \left( {\begin{matrix}\text{Average} \\\text{Luminance~~of}\end{matrix}\mspace{20mu} 1{◯3◯5◯7◯9◯}} \right)}} & (3)\end{matrix}$

In addition, light leakage was visually evaluated.

EXAMPLE 1

After dissolving 25 parts by weight of cyclic-olefin-based resin (Zeonor1600R available from Zeon Corporation) in 75 parts by weight of a mixedsolvent of xylene, cyclohexane, and toluene (1:1:1 mixing ratio byweight), a film was fabricated by solution casting. Both sides of theresulting film were then subjected to a corona discharge treatment at atreatment intensity of 100 W/m²/min in air, and a mixed solution ofpolyester polyol (Seikadyne LB available from Dainichiseika Color andChemicals Mfg. Co., Ltd.) and polyisocyanate (Seikadyne 3500A availablefrom Dainichiseika Color and Chemicals Mfg. Co., Ltd.) (1:11 mixingratio by weight) was coated on one surface of the film so that thethickness after drying was 0.2 μm and allowed to dry. Thus a protectivefilm with an anchor coat agent coated thereon having a thickness of 50μm, a width of 550 mm, and a length of 200 m was obtained. (Note that,immediately before winding the film, hot air at a temperature of 120° C.was introduced to the film for 10 seconds while the film was under adraw ratio of −0.2% between rollers, and distortions of molecular chainsin the cyclic-olefin-based resin were thereby corrected and the residualshrinking percentage was reduced.)

The water absorption of the protective films obtained in such a mannerwas 0.01%, the water vapor permeability was 3.0 g/m²/24 hours, andwetting tension was 600 μN/cm (23° C.). The residual amount of solvent,the surface shrinkage percentage, and the optical in-plane retardationR₀, R, and R−R₀ are shown in Table 1.

EXAMPLE 2

A PVA film (Kuraray vinylon film VF-9X75R available from Kuraray Co.,Ltd., thickness 75 μm) was immersed for 5 minutes in an aqueous solutionthat is 5000 parts by weight of water, 35 parts by weight of iodine, and525 parts by weight of potassium iodide such that the iodine wasadsorbed. After then uniaxially stetching the film in the longitudinaldirection to about 4.4 times in a 4% by weight of aqueous solution ofboric acid having a temperature of 45° C., the film was dried whileunder tension to obtain a polarizing film.

Next, the following process was carried out. The polarizing film and thepair of protective films obtained in Example 1 were arranged on top ofone another with a 5% aqueous solution of PVA interposed therebetweenserving as an adhesive and with the anchor coat sides of the protectivefilms facing either side of the polarizing film. The aqueous solution ofPVA had an average degree of polymerization of 1800 and a degree ofsaponification of 99%. The structure was then secured between a rubberroller and a metal roller (the rubber roller has a diameter of 200 mm,the metal roller has a diameter of 350 mm, line pressure is 10 kg/cm)and wound in such a manner that the thickness of an adhesive layer thatresults after drying is 1 μm. The structure was left in the wound state(length of 100 m) for 24 hours in a chamber having a temperature of 40°C. The results of the evaluation of the resulting polarizing plate areshown in Table 2.

EXAMPLE 3

Protective films were obtained in the same manner as in Example 1,except that a solution of 30 parts by weight of cyclic-olefin-basedresin (Zeonex 490K available from Zeon Corporation), 1 part by weight ofplasticizer (isodecyl adipate available from Kao Corporation) dissolvedin 69 parts by weight of xylene was used for the casting solution.

The water absorption of the protective films obtained in such a mannerwas 0.01%, the water vapor permeability was 2.9 g/m²/24 hours, andwetting tension was 600 μN/cm (23° C.). The residual amount of solvent,the surface shrinkage percentage, and the optical in-plane retardationR₀, R, and R−R₀ are shown in Table 1.

A polarizing plate was obtained in the same manner as Example 2 usingthese protective films. The results of the evaluation of the polarizingplate are shown in Table 2.

EXAMPLE 4

Using a cyclic-olefin-based resin (Zeonex 490 K available from ZeonCorporation), a film having a thickness of 50 μm was obtained by theextrusion molding with T-die (a T-die method), and protective films wereobtained in the same manner as Example 1 by employing a corona dischargetreatment and applying an anchor coat (extrusion temperature of 300° C.,take-up roller surface temperature of 130° C., immediately beforewinding the film, hot air at a temperature of 125° C. was introduced tothe film for 10 seconds while the film was tinder a draw ratio of −0.2%between rollers).

The water absorption of the protective films obtained in such a mannerwas 0.01%, the water vapor permeability was 3.0 g/m²/24 hours, andwetting tension was 600 μN/cm (23° C.). The residual amount of solvent,the surface shrinkage percentage, and the optical in-plane retardationR₀, R, and R−R₀ are as shown in Table 1.

Meanwhile, a polarizing film was obtained by the following method.Specifically, a PVA-based film (Kuraray vinylon film VF-9X75R availablefrom Kuraray Co., Ltd., thickness 75 μm) was uniaxially stretched in thelongitudinal direction to 3.4 times (change in thickness) by rolling thefilm between heated metal rollers (temperature of 110° C., diameter of350 mm, pressure of 170 kg/cm), and both ends of the film were trimmedoff by approximately 10 mm respectively. The film was again uniaxiallystretched to 1.2 times (change in thickness) between heated metalrollers (temperature of 110° C., diameter of 350 mm, pressure of 190kg/cm). The film was then immersed for 30 seconds in an aqueous solutionof iodine (a solution in which 18 parts by weight of iodine and 288parts by weight of potassium iodide are dissolved in 3600 parts byweight of water) while under tension and excess was removed using asqueezing roller. The film was then immersed in a 60° C. aqueoussolution of boric acid (a solution in which 600 parts by weight of boricacid, 3 parts by weight of iodine, and 48 parts by weight of potassiumiodide are dissolved in 12000 parts by weight of water) for 5 secondswhile under tension, and excess was removed using a squeezing roller.Finally, the film was dried while under tension, whereby a polarizingfilm was obtained.

A polarizing plate was then obtained in the same manner as Example 2using this polarizing film and the protective films described above.

The results of the evaluation of the polarizing plate are shown in Table2.

TABLE 1 Units Example 1 Example 3 Example 4 Residual amount of ppm 1,0000 0 solvent Surface shrinkage % 0.12 0.05 0.16 percentage In-plane R₀ nm0.2 0.2 0.3 retardation R nm 3.7 0.3 4.5 R—R₀ nm 3.5 0.1 4.2

TABLE 2 Units Example 2 Example 3 Example 4 Single Transmissivity % 41.941.9 42.6 Polarization efficiency % 99.9 99.9 99.9 Retention of — 1.001.00 1.00 polarization efficiency Hue b Initial value — 2.23 2.31 2.73After wet — 2.89 2.85 2.91 heating Hue a Initial value — −0.70 −0.68−0.78 After wet — −0.90 −0.96 −0.82 heating Amount of light — 1.54 1.291.68 leakage Visual Evaluation of — None None None Light Leakage

COMPARATIVE EXAMPLE 1

A polarizing plate was obtained in the same manner as Example 2 usingprotective films obtained in the same manner as Example 1, except that acorona discharge treatment was not carried out. The results of theevaluation of this polarizing plate are shown in Table 3.

COMPARATIVE EXAMPLE 2

A polarizing plate was obtained in the same manner as Example 1 andExample 2, except that an anchor coat was not applied to the protectivefilms and an emulsion-type, 2-part epoxy acrylic-based adhesive (thebase resin is E-Tec Emulsion AE 943, available from Japan SyntheticRubber Co., Ltd. and the curing agent is Aquanate 100, available fromNippon Polyurethane Industry Co., Ltd. (10:1 mixing ration by weight))was used for the adhesive. The results of the evaluation of thispolarizing plate are shown in Table 3.

COMPARATIVE EXAMPLE 3

A polarizing plate was obtained in the same manner as ComparativeExample 2, except that a corona discharge treatment was not carried outon the protective films. The results of the evaluation of thispolarizing plate are shown in Table 3.

TABLE 3 Comparative Comparative Comparative Units Example 1 Example 2Example 3 Single Transmissivity % 41.9 41.9 41.9 Polarization efficiency% 99.9 99.9 99.9 Retention of — 1.00 1.00 1.00 polarization efficiencyHue b Initial value — 2.46 2.78 2.18 After wet — 4.36 4.40 4.67 heatingHue a Initial value — −0.70 −0.90 −0.76 After wet — −0.04 −0.31 −0.06heating Amount of light — 2.49 2.55 2.60 leakage Visual evaluation of —small small small light leakage amount amount amount

COMPARATIVE EXAMPLE 4

Protective films having differing amounts of change in optical in-planeretardation were fabricated using the same casting solution as thatemployed in Example 1. The residual amount of solvent, the surfaceshrinkage percentage, and the optical in-plane retardation R₀, R, andR−R₀ are shown in Table 4. Using the protective films, a polarizingplate was then obtained in the same manner as Example 2. The results ofthe evaluation of this polarizing plate are shown in Table 5.

COMPARATIVE EXAMPLE 5

Protective films having differing amounts of change in optical in-planeretardation were fabricated using the same casting solution as thatemployed in Example 3. The residual amount of solvent, the surfaceshrinkage percentage, and the optical in-plane retardation R₀, R, andR−R₀ are shown in Table 4. Using the protective films, a polarizingplate was then obtained in the same manner as Example 2. The results ofthe evaluation of the polarizing plate are shown in Table 5.

TABLE 4 Comparative Comparative Units Example 4 Example 5 Residualamount of ppm 8000 0 solvent Surface shrinkage % 1.05 1.50 percentageIn-plane R₀ nm 0.9 3.3 retardation R nm 10.2 14.7 R-R₀ nm 9.3 11.4

TABLE 5 Comparative Comparative Units Example 4 Example 5 SingleTransmissivity % 41.9 41.9 Polarization efficiency % 99.9 99.9 Retentionof — 1.00 1.00 polarization efficiency Hue b Initial value — 2.26 2.32After wet — 2.91 2.88 heating Hue a Initial value — −0.71 −0.68 Afterwet — −0.97 −0.99 heating Amount of light — 6.91 7.40 leakage Visualevaluation of — Yes Yes light leakage

INDUSTRIAL APPLICABILITY

The present invention makes it possible to provide a polarizing platehaving high durability and high polarization efficiency with which thethree factors that contribute to a degradation in liquid crystal displayperformance under a high humidity/high temperature environment, drop inpolarization efficiency, hue shift, and light leakage, substantially donot occur.

1. A polarizing plate comprising a polarizing film made ofpolyvinyl-alcohol or a derivative thereof, a protective film mainlycomposed of a resin made of cyclic-olefin or a derivative thereof andlaminated on at least one side of the polarizing film, an anchor coatagent layer, and an adhesive layer: wherein the anchor coat agent layerand the adhesive layer interposed between the polarizing film and theprotective film; wherein the amount of change in optical in-planeretardation of the protective film is 5 nm or less after 24 hours in anatmosphere of 80° C., and the wetting tension of the surface to belaminated of the protective film is 500 μN/cm (23° C.) or more; whereinthe anchor coat agent is made of a polyester polyol and polyisocyanate;and wherein the adhesive is made of polyvinyl-alcohol or a derivativethereof.